1. Field of the Invention
The present invention relates to an electrode structure of a display panel and an electrode forming method, and more particularly, to an electrode structure of a display panel, for example, a plasma display panel (PDP), a liquid crystal display panel (LCD), an electro luminescence display (EL) or the like, in which electrodes are formed on a substrate through etching, and an electrode forming method.
2. Description of the Related Art
In a display panel of this kind, generally, electrodes are often formed through etching. In the case where the electrodes are to be formed on the substrate through etching, first, a layer of an electrode material such as ITO, SnO2, Cr, Cu or Ag is uniformly formed over the whole surface of the substrate by evaporation, sputtering or printing such as slot coating, then a resist pattern having a geometry of the electrodes is formed on the electrode material layer by photolithography or the like, and the electrode material layer is etched by pouring an etching solvent like a shower over the resist pattern, i.e., by a so-called spray etching.
In recent years, particularly, a so-called conveyer type inline manufacturing system has been the mainstream of display panel manufacturing apparatus as mass production has been demanded. In the inline manufacturing system, processing is continuously carried out while delivering a panel substrate on a conveyer line. For this reason, the spray etching is also carried out by spraying the etching solvent sequentially onto substrates by a spray device provided in a fixed position while delivering the substrates through the conveyer line.
In the above-mentioned display panel, electrodes having a geometry as shown in FIG. 12 are formed on the substrate, for example. FIG. 12 shows an example of electrodes formed on a glass substrate on a front face side of a 3-electrode surface discharge type PDP. In this PDP, a plurality of pairs of electrodes X and Y for generating a main discharge (surface discharge) for display are provided in a horizontal direction on a central part (display region) of a substrate 11. These electrodes X and Y are divided into a plurality of blocks and are collected and converged for each block on ends of the substrate 11 (outside the display region).
In this example, the electrodes X are converged on one side of the substrate 11 (the left side in the figure) and the electrodes Y are converged on the other side of the substrate 11 (the right side in the figure). The electrodes X and Y are connected to flexible cables 34 at terminal portions 33 on a substrate end on said one side and on a substrate end on said other side, respectively, with use of an anisotropic conductive adhesive or the like and are connected to drivers.
In FIG. 12, for simplicity of description, eight display lines (a display line represented by a pair of electrodes X and Y) form one block (or group) and the electrodes X and Y of each block are converged on the terminal portions 33 on one side and on the other side. 12. In an actual display panel having 480 display lines, for example, the display lines are divided into four blocks, each block having 120 display lines, through the division of the display line depends upon the performance of drivers. In each of the blocks, 120 electrodes X and 120 electrodes Y are converged on the terminal portions 33 on one side and on the other side and are connected to the flexible cables 34 at the terminal portions 33, respectively.
In the above-mentioned display panel, as the size is increased and high definition is sought for, the width of electrodes is reduced. Consequently, the shape and the dimension of the electrodes obtained after etching are required to have higher precision and uniformity.
However, when the electrode material layer is etched by the spray etching method while delivering the substrate by means of the inline manufacturing system, the etching solvent is excessively supplied to a block boundary portion B of the resist pattern formed on the electrode material layer and the electrode material layer is over-etched in this portion. This problem is now described.
FIG. 13 is a view illustrating the details of an end of the substrate on which the electrodes X and Y are formed. Hereinafter, for convenience, rectilinear portions of the electrodes X and Y arranged in almost parallel in the display region of the substrate will be referred to as discharge electrode portions 51, and oblique portions of the electrodes X and Y which extend from the discharge electrode portions 51, converge in a predetermined number for each block and reach the terminal portions 33 at the end of substrate will be referred to as lead electrode portions 52.
As shown in FIG. 13, at the end of the substrate, the discharge electrode portions 51 of either X or Y electrodes of the electrode pairs alone (for example, only the Y electrodes) are led out by the lead electrode portions 52 and reach the terminal portions 33. Consequently, with regard to the Y electrodes, electrode distances between the electrodes are smaller in the terminal portions 33 than in the display region. In the block boundary portion B, however, since the lead electrode portions 52 of Y electrodes in adjacent blocks extend obliquely in such directions as to keep away from each other (i.e., in opposite directions) with the block boundary portion B interposed therebetween, the electrode distances are greater in the terminal portions 33 than in the display region. Furthermore, an electrode interval (a gap) between the electrodes X and Y of each electrode pair which acts as a discharge slit (discharge portion) is smaller than the electrode distances in the terminal portions, and an electrode interval (a gap) between the electrodes X and Y of adjacent electrode pairs which acts as an inverse slit (non-discharge portion) is greater than the electrode distances in the terminal portions. In other words, the electrode distances are little different in the central part of the substrate and are much greater in the block boundary portions at the end of the substrate. This difference in the electrode distances (i.e., in the density of the electrodes) at the end of the substrate causes a problem during etching.
FIG. 14 is a view illustrating the details of an end of the substrate on which the resist pattern for forming the above-described electrodes is provided. As shown in FIG. 14, when the resist pattern for the electrodes, that is, a resist pattern 51a for forming the discharge electrode portions, a resist pattern 52a for forming the lead electrode portions and a resist pattern 33a for forming the terminal portions, is provided and the spray etching is carried out while delivering the substrate 11 in a direction of an arrow K, a flow in a relative direction shown by an arrow F is generated in the etching solvent for the following reason.
FIG. 15 is a view illustrating a section taken along the line A-Axe2x80x2 in FIG. 14. In general, the resist patterns 51a, 52a and 33a have hydrophobicity and has the property of repelling etching solvent 36. For this reason, the etching solvent 36 does not get on the resist patterns 51a, 52a and 33a easily and swells over the electrode material layer 31. Accordingly, the etching solvent 36 flows in the direction shown by the arrow F without getting over the resist patterns 51a, 52a and 33a. 
In FIG. 14, attention will be paid to the block boundary portion B of the resist pattern. At the substrate end, the interval between terminal electrodes in the block boundary portion is larger than the interval between terminal electrodes which are not positioned in the block boundary portion, and has a larger area for receiving the etching solvent. Consequently, the inflow of the etching solvent into the block boundary portion B is larger. In the display region, however, the electrode interval in the block boundary portion B is equal to the electrode distances of other electrodes. Accordingly, when the etching solvent, flowing in the F direction at the substrate end, concentrates along the resist pattern 52a for forming the lead electrode portions and flows into the display region, the inflow of the etching solvent increases in the display region, so that a flow velocity is increased.
As shown in FIG. 15, therefore, an etching speed of a part of the electrode material layer 32 positioned in the block boundary portion B is larger than that of a part thereof which is not positioned in the block boundary portion B. As a result, the discharge electrode portions 51 of the electrodes (shown as shaded in FIG. 14) positioned in the block boundary portion B are over-etched as compared with the discharge electrode portions 51 of the electrodes which are not positioned in the block boundary portion B and thus have smaller widths.
FIG. 16 corresponds to FIG. 15, showing the shape of the electrodes after etching. As shown in FIG. 16, the discharge electrode portions 51 (shown as shaded in FIG. 16) of the electrodes positioned in the block boundary portion B are formed to be narrower than the discharge electrode portions 51 of the electrodes which are not positioned in the block boundary portion B. That will be a cause of uneven display on the finished display panel.
As shown in FIG. 13, furthermore, the electrodes to be conveyed (the Y electrodes in FIG. 13) are provided obliquely such that the electrodes of adjacent blocks keep away from each other in the block boundary portion B at the end of the substrate. Therefore, the interval between the adjacent electrodes in the block boundary portion B is larger than the electrode distances in other portions. Consequently, a coupling capacity between the electrodes having a larger electrode interval is different from that between the electrodes having smaller electrode distances. Thus, electrical characteristics also have nonuniformity.
In consideration of such circumstances, it is an object of the present invention to provide an electrode structure of a display panel in which a dummy electrode for limiting the flow of etching solvent is provided in a block boundary portion at a substrate end to prevent excessive etching of an electrode material layer positioned in the block boundary portion and after manufacture, the dummy electrode is utilized also for correction of nonuniform coupling capacity, thereby eliminating the nonuniformity of electrical characteristics which would otherwise be involved with the discontinuity in the intervals between terminals, and an electrode forming method.
The present invention provides an electrode structure of a display panel comprising a plurality of electrodes formed on a substrate constituting the display panel, the electrodes including display electrode portions provided in almost parallel in a central part of the substrate and oblique lead electrode portions converged in a predetermined number for each block from the display electrode portions to reach terminal portions at an end of the substrate, and a dummy electrode provided between two oblique lead electrode portions extending in different directions in a block boundary portion for limiting a flow of an etching solvent into the block boundary portion during etching when the electrode are formed.
According to the present invention, a fine electrode pattern can be fabricated more uniformly with high precision. Consequently, it is possible to prevent display unevenness in the block boundary portion. Moreover, in the case in which a coupling portion for coupling the dummy electrode and the lead electrode portion is provided, the coupling capacity of the electrodes is almost equal in all the electrodes. Therefore, it is possible to obtain a display panel having uniform electrical characteristics.
These objects as well as other objects, features and advantages of the present invention will become more apparent to those skilled in the art from the following description with reference to the accompanying drawings.